3.1.3 Lipids - Triglycerides, Phospholipids and the Emulsion Test Flashcards
Which 3 elements do lipids contain?
Carbon
Hydrogen
Oxygen
Which part of a phospholipid is hydrophilic?
The phosphate ‘head’
Identify the molecule
Polyunsaturated fatty acid
What does hydrophobic mean?
water hating
How does the structure of triglycerides relate to their properties?
- High ratio of carbon-hydrogen bonds make them an excellent energy source
- Low mass to energy ratio- animals don’t have to carry a heavy energy store around.
- Non-polar molecules are insoluble in water so they do not affect osmosis in cells.
- High ratio of hydrogen to oxygen atoms so water released when trigylcerides are oxidised. Good for animals in deserts.
Identify the molecule
Monounsaturated fatty acid
Identify the molecule
Phosphate molecule
What state do monounsaturated and polyunsaturated fats take at room temperature?
Liquid - they are oils.
What is mean by a saturated fatty acid?
A fatty acid that contains no double bonds between the carbon atoms
Identify the molecule
Glycerol
Phospholipids are p___________ molecules
polar
What does the following describe:
- Add 2cm3 of food and add to a test tube.
- Add 5 cm3 of ethanol
- Shake the tube thoroughly to dissolve any lipid.
- Add 5cm3 of water and shake gently
- A cloudy-white colour indicates a positive result.
The emulsion test for lipids
What state do saturated lipids take at room temperature?
Solid - they are fats
What is meant by a polyunsaturated fatty acid?
A fatty acid that contains more than 1 double bond between its carbon atoms.
What does hydrophilic mean?
attracted to water
What type of bond forms between glycerol and fatty acid molecules?
Ester bond
Identify the molecule
Triglyceride
Identify the molecule
Saturated fatty acid
What type of reaction takes place when a fatty acid molecule is removed from a glycerol molecule?
Hydrolysis
What type of reaction takes place when a glycerol molecule joins with a fatty acid molecule?
Condensation reaction
Describe how you would carry out an emulsion test for lipids
The emulsion test for lipids:
- Add 2cm3 of food and add to a test tube.
- Add 5 cm3 of ethanol
- Shake the tube thoroughly to dissolve any lipid.
- Add 5cm3 of water and shake gently
- A cloudy-white colour indicates a positive result.
Which part of a phospholipid is hydrophobic?
The fatty acid ‘tails’
What decides the properties of different fats and oils?
Variations in their fatty acid chains
List the roles of lipids in living organisms.
- Cell membranes
- Energy store
- Waterproofing
- Heat insulation
- Electrical insulation
- Protection of organs e.g. kidneys
Why are triglycerides called triglycerides?
They contain 1 glycerol molecule (glyceride) and 3 fatty acids (tri)
What is meant by a monounsaturated fatty acid?
A fatty acid that contains 1 double bond between 1 pair of its carbon atoms.
Describe the structure of a phospholipid
1 glycerol molecule attached to
2 fatty acid molecules and
1 phosphate molecule
How does the structure of phospholipids relate to their properties?
- Polar molecules - meaning that they can form a barrier (cell membrane) between water inside and outside a cell.
- The phospholipid can form glycolipids by combining with carbohydrates. These are important in cell recognition.
Name the 2 main groups of lipid
Triglycerides (fats and oils)
Phospholipids
What happens when a phospholipid is placed in water?
The hydrophilic head positions itself towards water.
The hydrophobic tail positions itself away from water
Identify the molecule
Phospholipid
List the characteristics shared by all lipids
- They contain: Carbon, Hydrogen and Oxygen
- Lower proportion of oxygen to carbon and hydrogen than carbohydrates.
- Insoluble in water
- Soluble in organic solvents e.g. alcohols
how do you test for lipids?
dissolve in alcohol, then
add water then
white emulsion shows presence of lipid
name the bond between the glycerol and the fatty acid chains in a lipid molecule
ester
How can you tell the difference between a fatty acid that is saturated and how which is not?
saturated FA have no double bonds between carbon atoms
what is the difference between a triglyceride and a phospholipid?
in a phospholipid, one FA is replaced with a phosphate
name the reaction to breakdown phospholipids to release the phosphate
hydrolysis
name the element found in all amino acids but not in triglycerides?
Nitrogen
Compare and contrast structure of triglycerides and phospholipids
Both have ester bond
both contain glycerol
fatty acids on both can be saturated or unsaturated
Both contain C, H, O but phospholipids have also P
Triglycerides have 3 FA, Phospholipds have 2 FA and 1 phosphate group
Compare and contrast the properties of triglycerides and phospholipids
Both insoluble in water
Triglycerides are hydrophobic/non polar but phospholipids have hydrophobic and hydrophillic (polar) regions
Phospholipids form a micelle bilayer but triglycerides dont
